. Preventive medicine and hygiene. direct ancestry of the germ cells ineach individual. The cells which make up thebodily structure may be regarded as the resultof so many offshoots which come to an end atthe death of the organism and have no progenyof their own. The minute study of the germ cells taken inconnection with modern experimental work onthe methods by which inheritance takes placeshows a strong tendency to confirm Weismannsviews, so far as the inheritance of distinct anddefinite characters is concerned. Wilson ^ has expressed Weismanns theory asfollows: It is a reversal of the true
. Preventive medicine and hygiene. direct ancestry of the germ cells ineach individual. The cells which make up thebodily structure may be regarded as the resultof so many offshoots which come to an end atthe death of the organism and have no progenyof their own. The minute study of the germ cells taken inconnection with modern experimental work onthe methods by which inheritance takes placeshows a strong tendency to confirm Weismannsviews, so far as the inheritance of distinct anddefinite characters is concerned. Wilson ^ has expressed Weismanns theory asfollows: It is a reversal of the true point ofview to regard inheritance as taking place from the body of the parentto that of the child. The child inherits from the parent germ cell, notfrom the parent body, and the germ cell owes its characters not to thebody which bears it, but to its descent from a preexisting germ cell ofthe same kind. Thus, the body is, as it were, an offshoot from the germcell. As far as inheritance is concerned, the body is merely the carrier. Fig. 62.—Wilsons The-ory of ixhehitanceModified by Lock (G,germ cells; S, somaticcells). ^Weismann, A.: Essays upon Heredity, 1889, and The EvolutionTheory. 1906. * Wilson: The Cell in Development and Inheritance, p. 13. PEINCIPLES OF HEREDITY 485 of the germ cells which are held in trust for coming generations. illustrates Wilsons theory of inheritance as modified by Lock. Mendels Law.—\\e are indebted to Mendel ^ for one of the mostimportant observations of biology—the most important, in fact, withreference to heredity. The essential factors of Mendels discovery are:(1) unit characters, (2) dominance, (3) segregation. By a unit charac-ter is understood any characteristic of an individual that is transmitted A Schematic Repkesentation of Mendels Law D .P^—great-grandparental generation D P^—grandparental generation. D \ / \/D(R) .P^—parental generation. F^—first filial (hybrid) generation. 2DDPure dominants DD IDD
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Keywords: ., bookauthorwh, bookcentury1900, bookdecade1910, booksubjecthygiene
